IBM Series 1 User Manual page 136

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Tbe teletypewriter adapter has two commands that must be
described before presenting timing diagrams of transmit and
receive operations. These two commands are:
RegQ. The byte of data contained in the receive
serializer-deserializer register is transferred to main
storage. In normal operation, an attention interrupt
indicates to the procesor that a data character has been
received and is in the receive register.
A
Read command is
then executed as a part of the interrupt service program.
The receive register is
then
free to be used in receiving
another character.
If
a second character is received before the first
character is read from the receive register, an overrun
occurs. The first character is still in the receive
register,
and
the second character is lost.
Wri1~. A byte
of data is transferred from main storage to
the transmit serializer-deserializer register, and the
internal clocking necessary to serially transmit the
character is initiated.
At stop-bit time of the transmission of this character,
a device-end interrupt signals the processor that character
transmission is complete and that the adapter is available
to accept another write command.
Figure 4-3 is
a
timing diagram for transmit operations.
"WH"
on
the figure denotes a write command accepted; a
circle .3 denotes the device-end interrupt;
and "I.A."
denotes interrupt acceptance by the processor.
TXO is the transmit time from initiation of a transmit
operation to posting of the device-end interrupt.
TXO
is
nine
bit times at the selected bit rate. At 9600 BPS (bits
per second), TID is 0.936 ms; at 100 BPS it is 81.9 ms. TL
is the transmit load time, measured from the posting
of
the
device-end interrupt to the time at which the interrupt is
accepted and another Write command can be issued to the
adapter without loss of rated performance.
TL
is two bit
times at the selected bit rate. For 9600 BPS
1
TL is 0.208
ms; at 110 BPS, it is 18.2 ms. If a new Write command is
executed within time TL, the character rate is determined by
the adapter clocking; that is, a new transmit operation, is
not initiated in less than time TL from the posting of the
device-end interrupt. The adapter however, is "write busy"
upon successful execution of the Write command. If a new
write command is delayed beyond time TL, the transmit
operation is initiated immediately upon successful receipt
of the Write command.
Teletypewriter Adapter q-13